The old Book of Lairs (I and II) are great for this. Cheap too (in PDF).
Thank you! These are very useful.L1 Secret of Bonehill: the keep and dungeon at bone hill can easily be dropped in a sandbox as its very self contained.
UK2 The Sentinel: Has 3 locations that you can scatter on a map; bandit camp , ruined villa, druid cave, that player can find or explore. No need to include the macguffin hunt as a pretext.
I've run this one three times. Once converted to 5E in an ongoing campaign, twice in B/X with some house rules, one of those a convention game. Lots of fun.I only have Knock #1. It's got a good one, "Praise the Fallen", in the back. Lots of gold, a fun little cult. I don't think there are many others though. It isn't worth picking up for the mods, but worth it as a general resource.